1. Field of the Invention
The present invention relates to a resin composition which has excellent thin-wall flowability and provides a molded article having excellent heat resistance and low warpage.
2. Description of the Related Art
Since a liquid crystal polyester is composed of a rigid molecule, a polydomain is formed which does not cause entangling and keeps liquid crystal condition even in molten condition, there is represented a behavior in which a molecular chain is extremely oriented along flowing direction by shearing in molding, therefore, the polyester is generally called a melted liquid crystal type (thermotropic liquid crystal) polymer. The liquid crystal polyester has extremely excellent melt flowing property because of this specific behavior, and has high temperature of deflection under load and continuous use temperature depending on the molecular structure, and deformation and blister do not occur even if it is immersed in a melted solder of 260.degree. C. or higher. Therefore, a resin composition prepared by filling a fibrous reinforcing material represented by a glass fiber and an inorganic filler represented by talc into a liquid crystal polyester, is a material suitable for electric and electronic parts in thin-wall or complicated portions, and for example, used for sealing a relay part, coil bobbin, connector, volume part, motor parts such as a commutator and separator, or elements such as a coil, quartz oscillator, IC chip and the like. However, in a recent trend of small and light articles, a product shape is further required to be thin, and the electric and electronic parts as described above are required to have further improved flowability with maintaining the conventional heat resistance and mechanical properties. For further improvement of flowability of a liquid crystal polyester, various investigations have been carried out. For example, Japanese Patent Application Laid-Open (JP-A) No. 57-40550 discloses that a blend composed of a complete aromatic polyester which forms a first anisotropic melt phase composed of a repeating unit comprising about 10 or more % by mole of naphthalene and a complete aromatic polyester which forms a second anisotropic melt phase, is a polymer blend showing anisotropic melt phase which does not manifest significant decrease in mechanical property (herein, it is well known to those skilled in the art that the complete aromatic polyester which forms an anisotropic melt phase has the same meaning as a liquid crystal polyester.). However, in this publication, there is no description at all regarding whether such a polymer blend improves flowability of the first or second complete aromatic polyester. JP-A 59-85733 discloses that extrusion molding property of a liquid crystal polyester is improved by blending small amount of a crystalline compound having low molecular weight (less than 1000) into the liquid crystal polyester. However, this publication does not describe possibility of improvement in flowability in injection-molding, and in general, such a compound having low molecular weight has low heat resistance, and therefore causes thermal decomposition in molding-processing and can not be used. JP-A 3-252457 discloses that flowability of a liquid crystal polyester is improved by adding small amount of an oligomer containing as a main component p-hydroxy benzoic acid to the liquid crystal polyester. However, this composition is not stable in heat resistance represented by solder heat resistance, and can not be used practically. JP-A 60-245632 discloses improvement in flowability by adding small amount of a polymer flowability modifier composed of terephthalic acid, p-hydroxy benzoic acid, hydroquinone, isophthalic acid and biphenyl to aromatic oxybenzoyl polyesters. However, there is neither description that this polymer flowability modifier is a liquid crystal polyester, nor description that this modifier has effect of improving flowability in injection-molding at all. Further, in the use for a connector, improvements in low warpage and heat resistance are intensively required in addition to the above-described improvement in flowability, and the above-described methods can not provide a material having flowability, low warpage and heat resistance in good proportion.